Note: Descriptions are shown in the official language in which they were submitted.
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HOT REDUCED COIL TUBING AND A METHOD FOR FORMING SAME
BACKGROUND OF THE INVENTION
I. Field of the Invention
[0002] The present invention relates to oilfield coilable metallic tubing for
use in wellbores,
tubular strings, pipelines, bores, and boreholes.
[0003] More particularly, the present invention relates to coilable metallic
tubing having an
improved interior contour, to tapered tubing and to a method and apparatus for
making such
coilable metallic tubing, where the apparatus includes a plurality of reducing
stations and the
method include the steps of passing a tubing stock through a plurality of
reducing stations to
form the coilable tubing having an improved interior contour and having any
desired outer
diameter (OD) and internal diameter (ID) and any desired taper.
2. Description of the Related Art
[0004] Coil tubing (CT) is typically a relatively long continuous length of
tubing that can be
run in and out of a wellbore, tubular string, pipeline, bore and boreholes. CT
is widely used in
the oil and gas industry for drilling, completion, production, and workover
operations.
Alternatively, CT may be used for control lines, umbilicals, and in other
applications
requiring relatively long and durable tubing. CT is commonly manufactured from
steel or
steel alloy. Accessories or tools may be affixed interior to, exterior to, or
at the end of, a
length of CT to assist in its use or enhance its utility. Such tools and
accessories include
nozzles, sensors, guides, drill bits, centralizers, pumps, motors, subs,
valves and the like. CT
may be coated interiorly or exteriorly with a variety of materials. Such
coating materials
include plastic compositions, composites of plastics and metal, rubberized
composites,
lubricants, known anti-corrosion treatments and the like. When not in use,
CT typically is stored on a spool or reel in various lengths up to, and
exceeding, 20,000 feet.
When used, the CT is pulled or uncoiled from a storage reel, straightened,
supported and
urged forward by an injector that positions the CT at a desired location. When
it is desired to
remove
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the CT, the CT is coiled again on a storage reel. When it is again desired to
position the CT, the
process is repeated. This repeated coiling and uncoiling introduces stresses
into the CT and
weakens it to the forces of handling and to the forces from the pressure of
fluids passing through
it. Because of the stresses imposed on the CT by repeated coiling and
uncoiling, by pressure
cycles, by tension and torque, and by other forces, lengths of CT are limited
to a specified
number of duty cycles to minimize the likelihood of a failure. Failures
sometime occur because
of defects in welding. These failures, although not as frequent as experience
has been gained,
can result in expensive delays and recovery operations.
[00051 It is typical for lengths of CT to have a constant outside or outer
diameter (OD) that
designates the CT's nominal or target size. For example, CT may be delivered
in the following
sizes: 1.0", 1.25", 1.5",1.75", 2.0", 2 3/8", 2 5/8", 2 7/8", 3.5", 4.0",
4.5". The wall thickness of
CT may be constant or may vary along its length as described in U. S. Patent
No. 4,629,218 in
the name of the same inventor as the present invention. CT with a varying wall
thickness is
sometimes known as "tapered tubing" and has some advantages that reduce the
likelihood of
failure.
[0006] Coiled tubing is manufactured byprocesses described in U. S. Patent
Nos. 4,863,091 and
5,191,911, both in the name of the same inventor as the present invention.
Among these now
known processes for manufacturing CT, one example is a process where rolls of
sheet steel,
known as master coils typically 4'to 6' wide and 1,000 to 3,500' long, are
sliced or slit into strips.
These strips are of a width necessary to make the particular CT size being
manufactured.
Ordinarily, the width of the strip corresponds to the circumference, and hence
relates to the OD
of, the CT. The
thickness of these strips may be constant or may vary gradually along the
length of the strip in
accordance with the teachings of U. S. Patent No. 4,629,218 in the name of the
same inventor
as the present invention. Tapered tubing may be manufactured from flat stock
whose thickness
varies along its length.
[0007] Prior to being fashioned into CT, it has been common to join strips of
flat feed stock by
a transverse weld. The trailing end of a first feed coil may be joined to the
leading end of a
second feed coil by butt (90B) or bias (off-90B) welding. In bias welding as
described in U. S.
Patent Nos. 4,863,091 and 5,191,911 both in the name of the same inventor as
the present
invention, an-angle other than 90B is used between the strips being joined,
and some advantages
are realized that reduce the likelihood of failure.
[0008] It is contemplated in the prior art that bias weld joints be made by
stopping the trailing
end of a first feed coil during a period of time when upstream portions such
as the leading end
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and center section of the flat stock of that same coil continue to be
processed in a tube forming
operation. Through the use of an accumulator and flat feed stock conditioner,
the trailing end of
a first feed coil may be stopped for a period of time long enough to achieve a
joining of that
trailing end to the leading end of a second feed coil, all while the upstream
portion of the first
feed coil is continuing to be formed into tubing.
[0009] Tubing formation may take place in a tube mill through a series of sub-
processes in
which the flat feed stock is heated to a plastic or semi-plastic temperature
and then formed into
the shape of tubing. The configuring of the flat stock into tubing usually
occurs through a series
of rollers that gradually urge the flat stock into an appropriate geometry.
The side edges of the
flat stock are urged together to achieve a substantially circular cross-
section and are welded
together. This welding together of the side edges of the flat feed stock forms
a longitudinal seam
weld along the ,entire
length of the CT. The longitudinal weld may be achieved through a variety of
known processes.
Electric resistance welding (ERW) has been used in the past with some success.
When ERW is
used, it is known to reach inside the coil tubing being formed and to scarf
away or remove the
internal longitudinal weld flash. Similarly, it is known to remove the
external longitudinal weld
flash.
[0010] Following tubing formation, the CT is subjected to heat treating and
cooling. Following
cooling the CT is spooled onto a takeup reel. The CT may comprise as many
lengths of flat feed
stock as are welded together and fed through the tube mill. The CT will have a
wall thickness
that is the same as the thickness of the feed stock that is fed into the tube
forming process. As
noted, this thickness may be constant or, alternatively, may vary to create
tapered tubing.
[0011] Although the prior art has produced CT that is generally satisfactory,
room for
improvement exists. The feed stock has a chemical and physical profile such
that the strength
and performance characteristics of the CT formed from the flat stock is known.
Degradations or
departures from the chemical and physical profile of the CT made from the feed
stock may occur
at the transverse weld of one length of feed stock to another or continuously
along the length of
the CT in the region of the longitudinal weld. The stresses introduced by
repeated coiling and
uncoiling of CT and from the forces imposed by injection and withdrawal of CT
from wellbores,
exacerbates the consequences of this condition. Although heat treating and
bias weld techniques
have improved the quality of continuous CT, failures still have occurred in
CT, especially along
the longitudinal weld and at the transverse weld. Thus, there is a need in the
art for improved
methods and apparatuses for forming CT with improved physical properties.
SUMMARY OF THE INVENTION
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[0012] The present invention undertakes to further improve the quality,
reliability, and
resistance to coiling and uncoiling stresses of relatively long lengths of
coiled tubing (CT).
The present invention utilizes widths of feed stock that are deliberately
selected to be in
excess of the circumference, and hence the outer diameter (OD) of the CT
produced according
to the prior art. In the manufacturing process of CT according to the present
invention, tubing
exiting the tube mill is introduced into a forging process that substantially
reduces the
deliberately oversized OD of the coil tubing in process to the nominal or
target OD. This
reduction in OD may take place by subjecting the tubing to a hot reduction
mill that subjects
the entire tubing to forging. This forging is believed to improve the quality,
strength,
reliability, resistance to coiling and uncoiling stresses, chemical resistance
and other physical
properties of the CT, particularly in the locations of the strip-to-strip
transverse welds and the
longitudinal seam weld. Further, in the present invention the speed in feet-
per-minute of CT
spooled onto the takeup reel is greater than the speed of flat stock entering
the tube mill. This
results in faster production times for the manufacture of CT.
[0013] In certain embodiments, the grain structure of the steel forming the CT
is improved
and made more homogeneous so that the regions of the transverse weld and the
longitudinal
weld are substantially identical to the remainder of the CT. The occurrence of
grain
disturbance at the transverse weld is minimized or substantially eliminated.
The interruption
of the grain profile at the longitudinal seam weld of tubing is minimized or
substantially
eliminated. The speed of processing is increased to deliver to the takeup reel
longer lengths of
CT with improved resistance to coiling and uncoiling stresses.
[0014] Certain embodiments are not limited to any individual feature or object
described
herein. Rather, the embodiments include combinations of features and objects
that distinguish
from the prior art in structure, function, and process. Features of the
invention have been
broadly described so that the detailed description that follows may be better
understood and
so that the contributions to the art may be better appreciated. Those skilled
in the art who have
the benefit of this invention, its teachings and suggestions, will appreciate
that the conceptions
of this disclosure may be used as a creative basis for designing other
structures, methods and
systems for carrying out and practicing the present invention.
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[00151 The present invention recognizes and addresses the noted problems of CT
failures and
long felt needs and provides a solution to those problems and a satisfactory
meeting of those
needs in its various possible embodiments and equivalents thereof. To one
skilled in this art
who has the benefit of this invention, its teachings, and suggestions, other
purposes and
advantages will be appreciated from the following description of preferred
embodiments,
provided for the purpose of disclosure, when taken in conjunction with the
accompanying
drawings. The detail in these descriptions is not intended to frustrate the
inventor's objective
in protecting this invention no matter how others may later disguise it by
variations in form or
additions of further improvements. The present invention is intended to
provide a new, useful,
and non-obvious improvement to continuous CT together with new, useful, and
nonobvious
methods and processes for making such CT.
[00161 Features of the present invention have been broadly described so that
the detailed
description that follows may be better understood and in order that the
contribution to the art
may be better appreciated. There are, of course, additional aspects of the
invention described
below.
[00171 An apparatus forging station is disclosed herein having a plurality of
stands, where
each stand is adapted to change at least one characteristic or property of a
length of tubing as
it passes through that stand. The characteristics or properties that are
subject to change in each
of the stations include an inner diameter (i.d. or ID), an outer diameter
(o.d. or OD), wall
thickness (WT), metallic microstructure (MMS), metallic temper (MT), or any
other metal
property or characteristic that can be changed during a heating process, a
cooling process, a
heating plus stretching process, a heating plus compressing process, a cooling
plus stretching
process, or a cooling plus compressing process. The stands are adapted to
change the
characteristics or properties by about 1% to about 10% per station. In this
way, the starting
tubing, after longitudinal and/or lateral welding, can be altered in a pre-
determined manner to
form a tubing having a desired OD, ID, WT, MMS and/or MT that are relatively
or
substantially constant over the entire length of the tubing, that change
continuously along the
entire length or any given length of the tubing followed by a length of tubing
where the
characteristics remain substantially constant, or tubing has lengths of tubing
that have
changing properties and lengths of tubing that have properties that are
substantially constant.
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The term substantially constant as used in this paragraph means that the value
of the property
or properties change less than about 10% over the lengths of tubing for which
the property or
properties are substantially constant. In certain embodiments, the changes
change less the 5%
over the lengths of tubing for which the property or properties are
substantially constant. In
certain embodiments, the changes change less the 2% over the lengths of tubing
for which the
property or properties are substantially constant. In certain embodiments, the
changes change
less the 1% over the lengths of tubing for which the property or properties
are substantially
constant.
[0018] Also disclosed is a method for producing coiled tubing having section
(a pre-
determined length of tubing) having variations in tubing properties, where the
method
includes the steps of forming tubing from a length of a flat metal sheet or
flat metal ribbon,
where the forming step converts the flat sheet into a tube with the two edges
of the sheet in a
close proximity. After the flat sheet have been formed into a tube, the edges
are welded
together to form a longitudinal seam. After or concurrent with the seam
welding step, weld
residue is scarfed from an outer and inner surface of the tube at the seam
weld. After scarfing,
the tubing is milled to produce a tubing having a desired tube profile and/or
properties, where
the profile and/or properties are substantially constant over the entire
length of the tubing,
varies over the entire length of the tubing, varies over one or more sections
of the entire
length of the tubing and are substantially constant over other sections of the
tubing. The
method can also include the steps of heating treating, tempering and/or
cooling the tubing
existing the milling step. The method can also include spooling the tubing
onto a reel for
storage and/or transport.
[0018a] According to one aspect of the invention there is provided a method of
making a
continuous length of tubing, the method comprising: (a) (i) providing a first
length of flat strip
stock having a leading end and a trailing end and a center section and further
having a width
and a thickness; (ii) providing a second length of flat strip stock having a
leading end and a
trailing end and a center section and further having a width and a thickness
that are
substantially the same as the width and the thickness of the first length of
flat strip stock; (iii)
trimming the trailing end of the first length of flat strip stock and the
leading end of the
second length of flat strip stock; (b) welding the leading end of the second
length of flat strip
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stock to the trailing end of the first length flat strip stock to form a
composite strip transverse
weld; (c) feeding the finished composite strip into a tube forming process to
form a tubing
having a first outside diameter and a first wall thickness by welding opposing
edges of the
composite strip to form a longitudinal weld; (d) introducing the tubing coming
out of the tube
forming process into a hot reduction mill at a first feed speed, where the hot
reduction mill
includes a plurality of stands; and wherein each stand includes a set of tube
engaging rollers,
an internal distance between the rollers within the set of tube engaging
rollers being
adjustable while the stand is positioned in the hot reduction mill; and
wherein each stand is
separated from its immediate successor and/or predecessor by a gap; and
wherein each stand
changes one or more properties of the tubing by an amount between about I% to
about 10%,
where the properties include outer diameter, inner diameter and metallurgical
properties; and
wherein each set of rollers has a roller orientation, and wherein the roller
orientation of one
set of rollers is rotated by an angle relative to the roller orientation of
another set of rollers,
the angle being selected to reduce, minimize or eliminate circumferential non-
uniformities in
the internal contour of the tubing; (e) reducing the outside diameter of the
tubing to a second
outside diameter less than the first outside diameter; (f) hot forging the
tubing; and (g)
withdrawing the tubing from the hot reduction mill at a second feed speed
greater than the
first feed speed.
[0018b] According to another aspect of the invention there is provided a
method of
manufacturing coiled tubing, the method comprising: (a) feeding a flat metal
strip into a tube
forming process to form a feed tubing by welding opposing edges of the
composite strip; (b)
introducing the feed tubing into a hot reduction mill at a first feed speed,
where the hot
reduction mill includes a plurality of stands, each stand including a set of
rollers oriented to
selectably engage the feed tubing as it passes through the hot reduction mill;
(c) adjusting
each set of selectably engaged rollers during operation of the hot reduction
mill to exert a
desired compressive force on the tubing passing through the hot reduction
mill; (d)
withdrawing the tubing from the hot reduction mill at a second feed speed; and
(e)altering at
least one property of the feed tubing as the tubing passes through the hot
reduction mill,
where the properties include an outer diameter, an inner diameter and a wall
thickness.
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10018c] According to another aspect of the invention there is provided a
method of
manufacturing coiled tubing, the method comprising: (a) feeding a flat metal
strip into a tube
forming process to form a feed tubing by welding opposing edges of the
composite strip; (b)
introducing the feed tubing into a hot reduction mill at a first feed speed,
where the hot
reduction mill includes a plurality of stands, each stand including (i) a
housing having an
aperture therethrough; (ii) a plurality of rollers, wherein each roller is
mounted on a slidable
mount within the housing; (iii) a first motor in communication with each
slidable mount, the
motor adjusts the positioning of the slidable mount toward a center of the
housing aperture or
away from the center of the housing aperture thereby adjusting a compressive
force exerted
by the rollers on the tubing passing through the housing aperture; and (iv) a
second motor in
communication with the rollers for adjusting the rotation speed of the rollers
such that all of
the rollers within each stand rotate at the same speed; (c) adjusting the
rotational speed of
each set of selectably engaged rollers using the second motor and adjusting
the compressive
force exerted by all of rollers in the stand to a predetermined compressive
force using the
second motor; (d) withdrawing the tubing from the hot reduction mill at a
second feed speed;
and (e) altering at least one property of the feed tubing as the tubing passes
through the hot
reduction mill, where the properties include an outer diameter, an inner
diameter and a wall
thickness.
[0018d] According to another aspect of the invention there is provided a hot
reduction mill for
making coiled tubing having a plurality of roller stands, each roller stand
comprising: (a) a
housing having an aperture therethrough; (b) a plurality of rollers, wherein
each roller is
mounted on a slidable mount within the housing; (c) a first motor in
communication with each
slidable mount, the motor adjusts the positioning of the slidable mount toward
a center of the
housing aperture or away from the center of the housing aperture thereby
adjusting a
compressive force exerted by roller on the tubing passing through the housing
aperture; and
(d) a second motor in communication with the rollers for adjusting the
rotation speed of the
rollers.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention can be better understood with reference to the following
detailed
description together with the appended illustrative drawings in which like
elements are
numbered the same:
[0020] Figure 1 is a schematic representation of a prior art system for
producing coil tubing;
[0021] Figure 2 is a schematic representation of a joining process of the
present invention;
[0022] Figure 3 depicts an alignment of the ends of strips to be joined;
[0023] Figure 3A depicts an alterative for an alignment of the ends of the
strips to be joined;
[0024] Figure 3B depicts another alternative for an alignment of the ends of
the strips to be
joined;
[0025] Figure 4 schematically depicts a welding process for joining two ends
of strip stock;
[0026] Figure 5 schematically depicts the welded ends of strip stock prior to
finishing or
dressing;
[0027] Figure 6 schematically depicts grinding away a portion of the upset
formed by a
welding process used to join the end of the strips;
[0028] Figure 7 schematically depicts rolling the transverse weld used to join
the strips to
help conform the geometry of that weld to the surrounding strip stock;
[0029] Figure 8 depicts the transverse weld following finishing or dressing;
[0030] Figure 9 schematically depicts heat treating the finished or dressed
transverse weld;
[0031] Figure 10 schematically depicts the flow of the strip stock through the
joining station
and
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then into a tube mill;
[0032] Figure 11 schematically depicts some of the steps used in the practice
of the present
invention including the step of forging the tubing that exits from the tube
mill;
[0033] Figure 12 depicts relatively large diameter, thick walled tubing
exiting the forging
station of Figure 11;
[0034] Figure 13 depicts relatively small diameter, thin walled tubing exiting
the forging station
of Figure 11;
[0035] Figure 14 depicts relatively small diameter, thick walled.tubing
exiting the forging
station of Figure 11;
[0036] Figures 15A D .depict schematically four embodiments of the tube
reducing stations
of this invention showing different numbers of stands;
[0037] Figure 15E schematically depicts the relative spacing of the stands in
the tube reducing
station;
[0038] Figures 16A&B schematically depicts details of an electric or hydraulic
stand;
[0039] Figure 17. schematically depicts details of a mechanical stand; and
[0040] Figures 18A H schematically depict varieties of tubing produced.
DE TAILED DESCRIPTION OF THE INVENTION
[0041] The inventor has found that coiled tubing can be produced from
oversized stock using
a hot mill reduction apparatus that is capable of producing a coiled tubing
having a substantially
circular interior contour, where the reduction occurs by passing the oversized
tubing through a
plurality of reducing stations that reduce an outer diameter, an inner
diameter and/or a wall
thickness of the feedstock about 5 to about 6% per station or stand. The
stands include at least
two and generally at least three tube engaging members or concaved rollers
mounted on separate
controllers that control the compressive force acting on the tubing at that
stancl.
[0042] In the prior art system 20 as depicted in Figure 1, a length of CT 22
could be made by
the following process. A first feed coil 24 of flat strip stock 26 is fed to
an accumulator 28, then
through a conditioner 30, and into a tube mill or tube former 32 following
which the tubing is
heat treated in a heat treater 34 and, following cooling, is spooled onto a
takeup reel 36. The first
feed coil 24 of flat stock 26 is fed through the system 20 until the trailing
end 38 of the first feed
coil 24 is reached. Thereafter, a second feed coil 40 is welded to the first
feed coil 24 by means
of a bias weld joint 42; and the process continues without interruption until
a desired leiigth of
CT 22 has been spooled onto the takeup reel 36. The accumulator 28 is
positioned so that the
tube mill 32 continues to function and tubing made from the leading end and
center section of
the first feed coil continues to be spooled onto the takeup reel 36 while the
trailing end 38 of the
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first feed coil 24 is stationary to enable the bias weld joint 42 to be
formed. During that time the
"slack" in the conditioner 30 and accumulator 28 combination provides the flow
ofmaterial into
the tube mill 32 while keeping the trailing end 38 of the first feed coil 24
stationary. This could
provide sufficient time to make a weld joint such as a bias weld joint 42 and
favorably position
the second feed coil 40 for continuous operation. The accumulator 28 and
conditioner 30, now
well known in the art, include rollers 44 that are positioned in slots 46 as
shown in Figure 2 that
extend to a full slack position, and when it is desired to stop the trailing
end of the reel, the
rollers 44 gradually move to the center line 48 (Figure 2) of the flat stock
feed path to provide
continuous feed of material to the tube mill 32. The tube mill 32 operates to
gradually urge the
flat strip stock into the configuration of a tube. This occurs in stages
through the use of rollers
(not shown) and dies (not shown) and the like that urge or cam the flat stock
26 into a circular
cross-section. This ultimately brings into proximity the left and right side
edges 50, 52
respectively as shown in Figure 3 of the flat stock 26 to achieve a closure of
the now formed
circular cross-sectioned tubing, and a longitudinal seam weld 54 as shown in
Figure =11 is made.
This longitudinal seam weld 54 typically is in the form of an electric
resistance weld (ERW). An
internal scarfing device 56 or other device may be used to reach into the
inside of the tubing
being longitudinally welded to remove excess internal weldment from the
longitudinal weld.
Similarly, an external scarfing device 58 or the like is used to remove excess
external weldment
from the longitudinal weld to dress the outside surface of the tubing. An
induction heater 60 may
be used to heat treat the tubing at a heat treater 34, and, following cooling,
which can occur in
a cooling station 35, the CT 22 is spooled onto a takeup reel 36.
[0042] In the present invention, there are some similarities to the known
process. That is, as
shown in Figure 2, an accumulator 62 may be used to stop the trailing end 38
of a first feed coil
64 in relation to the movement of the leading end 41 and a center section 43
of the flat stock 26
through a tube former or tube mill 32. Such an accumulator 62 may serve to
condition the flat
stock 26 to improve the handling of the flat stock through the tube mil 32.
When the trailing end
38 of the first feed coil 64 is reached, the accumulator 62 is activated to
stop the movement of
the trailing end 38 to facilitate joining of that trailing end 38 to the
leading end 39 of a second
feed coil 66 at a joining station 70. Typically both the trailing end 38 of
the first feed coil 64 and
the leading end 39 of the second feed coil 66 are cut and trimmed or "dressed"
to facilitate
joining. A variety of joining techniques maybe used in the joining station 70
to join the end edge
72 of the trailing end 38 of the first feed coil 64 to the lead edge 74 of the
leading end 39 of the
second feed coil 66. In one preferred embodiment, the trailing end 38 of the
first feed coil 64 is
joined to the leading end 39 of the second feed coil 66 by a process known as
forge welding as
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shown in Figure 3, Figure 3A, Figure 3B, Figure 4 and Figure 5. A forged weld
76 utilizes
some energy or power source 78 to create a localized zone of intense heat 80
at the interface or
juncture 82 of the two lengths of strip stock. In one preferred embodiment as
depicted in Figure
4 and Figure 5, the two lengths of strip stock are urged toward each other
after heating 80 has
occurred to achieve the forged weld 76. This may result in there being a
slight upset 84 of
material at the interface 82 of the two lengths of strip stock. The axial
grain 86 of the steel or
steel alloy material comprising the strip stock is disturbed at the region of
the forged weld 76.
This results in the grain turning upwardly to form what is known as "end
grain" 88 at the forged
weld at and around the juncture 82 of the two lengths of strip stock. The
misalignment of the
grain of the steel or steel alloy at this location 82 can impart some
undesirable characteristics to
the CT 22 thereafter fashioned from the flat strip stock 26. For example, it
is believed that the
end grain 88 is more vulnerable to corrosion or may not display the same
physical characteristics
of the remaining steel that enjoys a substantially coherent axial alignment as
depicted by the
axial grain 86.
[0043] The forged weld 76 that is achieved to join the lengths of strip stock
may have the end
edge 72 and the lead edge 74 aligned with the side edges 50, 52 at
substantially 90 to achieve
a "butt weld" or maybe at some angle other than 90 to achieve a "bias weld".
See U. S. Patent
No. 4,863,091 and 5,191,911, both in the name ofthe same inventor as the
present invention, for
examples of a bias weld. In addition to 90 butt welding or bias welding to
join the trailing end
38 of the first reel to the leading end 39. of a second reel, a 90 offset
weld 90 may be used as
shown in Figure 3A. The 90 offset weld requires that a right-angled notch 91
be formed in both
the trailing end 38 and leading end 39 of the strips to be jointed.
Alternative geometries such as
right-angled multiple notches (not shown), step notches (not shown), mortises
(not shown), or
t-slots (not shown) may be used. A further alternative is the 90 ramp weld 93
that utilizes a
ramped end edge 72' and a cooperating ramped lead edge 74'. As shown in Figure
3B, both
ramped edges 72, 74' are aligned with the side edges 50, 52 at substantially
90 . The 90 offset
weld 90, the 90 ramp weld 93, and the other alternatives noted are
alternative preferred
embodiments, and may be achieved by using forged welding, TIG welding, or any
other
satisfactory welding technique.
[0044] In any event, it is desirable to conform the geometry of the transverse
weld to the
surrounding material. That is, the upset 84 formed, whether by weldment or
parent material,
along the top 92 and bottom 94 of the interface 82 as shown in Figure 8 may be
removed, for
example, by grinding with grinders 96 as shown in Figure 6 and/or by rolling
with rollers 98 as
shown in Figure 7. Similar dressing may take place with respect to the left
side edge 50 and the
CA 02731337 2011-02-07
-10-
right side edge 52 of the composite strip formed as a result of the transverse
weld. An objective
in the practice of the present invention is to achieve a weld joint having a
geometry that
corresponds generally to the thickness and width of the surrounding flat strip
stock 26. Dressing
the weld joint helps achieve an uninterrupted flow of fluid through the CT and
minimizes the
likelihood of localized erosion or corrosion at the site of the transverse
weld joint. The geometry
should be conformed to the greatest extent feasible considering the time
provided by the
accumulator 62 to hold stationary the trailing end 38 of the first feed coil
64. A forged weld 76
and its following dressing steps can be accomplished at the joining station 70
within the time
allotted as shown in Figure 10.
[0045] In addition, heat treating by a heat treater 34 of the forged weld 76
may impart further
favorable characteristics to the juncture 82 as schematically depicted in
Figure 9. The heat
treating may be. accomplished by induction heating by an induction heater 60
to raise the
temperature of the composite welded strip at the location of the transverse
weld to a temperature
to achieve improved characteristics of the weld joint in terms of its
chemistry, metallurgy, and
physical profile.
[0046] The joining station 70 may include a quality control inspection step.
The quality control
inspection step may utilize x-rays, or ultrasound, or other non-destructive
testing techniques
known in the art for detecting flaws in welds. It is believed that the
selection of a forged weld
can result in a fast and relatively defect free joining of the trailing end 38
of the first feed coil
64 to the leading end 39 of a second feed coil 66. In alternative embodiments,
the transverse
weld could be achieved by the use of high frequency welding, TIG welding,
plasma arc welding,
or ERW. Of course, similar joining steps may take place between subsequent
feed coils, for
example, between a second and a third feed coil (not shown), between a third
and a fourth feed
coil (not shown), and so forth, until a desired length of CT is spooled onto
the takeup reel 36.
[0047] After the joining occurs between feed coils at joining station 70, the
accumulator/conditioner 62 may be adjusted to resume feed of flat stock from
the second feed
coil 66. In this manner, there is no interruption in the operation of the tube
mill 32 during
changeover of feed coils, and flat stock 26 is continuously fed to the tube
mill without having
to stop the tube mill.
[0048] The tubing exiting from the tube mill 32 has as its circumference a
dimension that is
substantially the same as the width of the flat stock 26 fed into the tube
mill. Within the tube
mill, there are sizing rollers and other known arrangements (not shown) to
conform the OD of
the tubing being made to a substantially uniform dimension within tolerance of
the operation of
the tube mill. The sizing arrangements may include sizing rollers or
stationary apertures or dies
CA 02731337 2011-02-07
-11-
that serve to remove any irregularities in the outside dimension of the tubing
that may be
inherent in the flat feed stock 26 or that may have been introduced during
processing.
[0049] Referring now to Figure 11, in the present invention, the width of the
flat feed stock 26
is deliberately selected to be substantially greater than the circumference
(and hence the OD) of
the CT 100 spooled onto the takeup reel 102. That is, the tubing that exits
the tube mill 32 is
deliberately of a greater diameter than the target or nominal OD of the CT 100
of the present
invention. The relatively large diameter tubing-in-process 104 that exits the
tube mill 32 is
introduced into a forging stage 106. This forging stage 106 may occur in a hot
reduction mill 1Q8
as shown in Figure 11. The hot reduction mill 108 is an apparatus that heats
the tubing-in-
process 104 to a temperature where its OD is substantially reduced through the
use of rollers
and/or dies (not shown) that forge the tubing-in-process 104 as the OD is
adjusted. This action
of heating and hot forging of the tubing-in-process '104 results in a
favorable realignment of the
end grain 88 in the region of the transverse weld that joined the trailing end
38 of the first feed
coil 64 to the leading end 39 of the second feed coil 66. In addition, the
forging action provides
a beneficial realignment of the grain structure in the longitudinal seam weld
54 and in the
regions therearound. In the forging process, there is an elongation or
stretching of the tubing-in-
process 104 in its semi-plastic state. This is accomplished through the use of
drive rollers 105
in the hot reduction mill 108 or downstream of the hot reduction mill 108,
sizing rollers (not
shown), or dies (not shown) that introduce axial tension into the tubing-in-
process 104 that
increases the speed or velocity of its travel through this stage of the
process. Therefore, the speed
of the tubing that exits the forging stage or hot reducing mill is faster than
the speed of the
tubing-in-process 104 that enters the forging stage or hot reduction mill. The
increase in speed
of processing results in CT 100 being spooled onto the takeup reel 102 at a
faster rate than the
rate of feed of flat stock 26 from the feed coil. It is believed that a
significant increase in
processing speed maybe accomplished when the teachings ofthe present invention
are followed.
[0050] The forged CT 100 exiting the forging stage or hot reducing mill may be
further heated
by a heater 110 and then quenched in a quenching bath 112 to achieve a quench-
and-temper heat
treatment. Following a quench-and-temper heat treatment the forged CT 100 may
be spooled
onto the takeup reel 102.
[0051] As depicted in Figures 11-14, in the forging process or hot reducing
mill, the wall
thickness (WT) and OD of the CT produced may have a variety of aspect ratios
(ratio of outside
diameter OD to inside diameter ID or ratio of outside diameter OD to wall
thickness WT). That
is, not only will the OD of CT 100 produced be different from the OD of the
tubing-in-process
104 exiting the tube mill 32, but also the wall thickness of the finished CT
100 may be the same
CA 02731337 2011-02-07
-12-
as, greater than, or less than the wall thickness of the tubing-in-process 104
exiting the tube mill
32. Within the forging stage or hot reduction mill, the temperature, speed of
drive, tension on
the tubing-in-process 104, rate of OD reduction, and other wall thickness
configuring
parameters, may be adjusted to select wall thicknesses over a range in
relation to the wall
thickness of the tubing-in-process 104 exiting the tube mill 32 or the
thickness of the flat stock
26.
[0052] In the prior art, when it was desired to change the OD of CT produced
in a tube mill, the
rollers and/or dies of the tube mill would be changed manually that resulted
in substantial delays
and expenditure of substantial labor to achieve the breakdown and turnover to
prepare the mill
for a CT of a different OD. With the present invention, no tear down of the
mill is necessary.
Rather, adjustments maybe made to the system without having to replace rollers
and the like and
without the need for substantial labor to prepare the system for the
manufacture of CT of a
different OD. This flexibility facilities manufacturing changes while the CT
forming process is
taking place.
[0053] For example, if it is desired to manufacture CT having a varying OD,
this may be
accomplished using the manufacturing process of the present invention. Such
tubing might have
a continuous or a varying wall thickness. That is, CT could be manufactured
having a constant
wall thickness, but a varying OD using the present invention. Alternatively,
CT could be
manufactured having both a varying OD and a varying wall thickness.
[0054] If it is desired to manufacture CT having different yield strengths,
the quench-and-temper
station may be selectively included in the process. This facilitates maldng a
continuous length
of CT that has a varying yield strength for applications where this would
provide operational and
economic benefits.
[0055] Referring now to Figures 15A-D, the milling station, forging station or
hot reduction mill
106 includes a plurality of coil tubing reducing units or stands 200. Looking
at Figure 15A, the
milling station 106 includes ten coil tubing reducing stands 200. Looking at
Figure 15B, the
milling station 106 includes fifteen coil tubing reducing stands 200. Looking
at Figure 15C, the
milling station 106 includes twenty coil tubing reducing stands 200. Looking
at Figure 15D,
the milling station 106 includes twenty six coil tubing reducing stands 200.
[0056] Although the exact number of stands 200 can be adjusted depending on
the nature of the
CT to be produced as defined by the outer diameter (OD), inner diameter (ID);
and/or wall
thickness (WT) of the produced tubing, the number of stands well generally be
sufficient to
achieve a desired result incrementally with each stand 200 changing the OD, ID
and/or WT by
about 1 to 10%. Moreover, the number of stands 200 can be set at the maximum
needed to
CA 02731337 2011-02-07
-13-
achieve a tubing the is changed the most for the particular installation. If
less stands 200 are
needed for a given tubing product, then the operator can simply turn off as
many stands as
desired.
[0057] In certain embodiments, the forging station 106 includes between 5 and
50 stands 200.
In other embodiments, the forging station 106 includes between 10 and 40
stands 200. In other
embodiments, the forging station 106 includes between 15 and 35 stands 200. In
other
embodiments, the forging station 106 includes between 20 and 30 stands 200. In
all these
embodiments, the number of active stands 200 will depend on the tubing being
produced, i.e.,
some of the stands may be idle. Each of the stands can be separately heated,
but generally it is
preferred that the stands are housed in a temperatures controlled room so that
the temperature
of the tubing passing through each stand can be in a desired region.
Alternatively, sets of stands
can be housed in temperature controlled rooms to maintain the temperature of
those stands at
desired temperature. In this latter alternative, the temperatures in each room
can be the same or
different. If the stands are heated separately, then the gap between the
stands can includes an
insulating or heated gap unit so that the tubing does not cool substantially
as it travels from one
stand to the next stand.
[0058] Each stand 200 is designed to achieve a given change in one or more of
the tubing
properties such as the OD, ID, WT, etc. Thus, the plurality of stands 200
accomplishes, a
systematic and incremental change in the tubing properties as the tubing is
being forged.
Generally, each stand 200 will change one or more properties by an amount
between about 1%
to about 10% depending on the desired process and the metallurgy of the strip
stock used and
upon the conditions within each of the stands 200. In certain embodiments,
each stand 200 will
change one or more properties of the entering tubing by an amount between
about 2% and about
8%. In certain embodiments, each stand 200 will change one or more properties
of the entering
tubing by an amount between about 4% and about 7%. In certain embodiments,
each stand 200
will change one or more properties of the entering tubing by an amount of
between about 5% and
about 6%.
[0059] Referring now to Figure 15E, an expanded view ofFigure 15A is shown to
illustrate the
gap between successive stands 200. Each stand 200 is displaced from its
immediate predecessor
and successor by a gap distance A between about 5" and about 30". In certain
embodiments, the
distance between successive stands is between about 511 and about 20". In
other embodiments,
the distance between successive stands is between about 5" and about 15". In
other
embodiments, the distance between successive stands is between about 8" and
about 12". In
other embodiments, the distance between successive stands is about 10".
Although the gap
CA 02731337 2011-02-07
-14-
distances can be the same (i. e., A, =A2=A3=A4= As = A6 = A7 = Ag = A9 = ... =
Ap ), the gap
distances can also be different (i.e., A, # A2 o A3 o A4 * AS o A6 o A7 o As *
A9 * ... * A,J, where
n is the total number of stands.
[0060] In the prior art, stands, that change one or more tubing properties,
alter the properties in
such a way that the inside contour of the tubing assume a substantially non-
circular contour
generally a hexagonal profile or contour. Such non-circular profiles or
contours have certain
disadvantages. The profiles can reduce the size of tools that can be inserted
into the tubing and
can imped flow characteristics of materials into and through the tubing. To
produce a tubing
with a substantially smooth and circular internal profile or contour, each
successive stand 200
is rotated relative to its predecessor by an angle sufficient to reduce,
minimize or eliminate
circumferential non-uniformities in the internal contour of the tubing.
Circular internal tubing
contours are evidenced by tubing having wall thicknesses (WT) that are
substantially uniform
around the circumference of the tubing at all locations along its length (even
though the wall
thickness may change along the entire length of the tubing or along certain
section lengths of the
tubing). The process that produces a substantially circular internal contour
also results in a
relaxation and smoothing of grooves formed during the scarfing process after
longitudinal or
lateral welding.
[0061] Depending on the number of tubing engaging member in each of the
stands, the rotation
angle between successive stands is such that the engaging member are rotated
by a desired angle
that does not result in the engaging member alignment being identical to its
immediate successor
or predecessor. For example, if each stand has three tubing engaging members,
then a rotation
by 120 results in an identical alignment of the engaging members. In certain
embodiments, for
stands that have three tubing engaging member, the angle of rotation between
successive stands
is between about 5 and about 115 or about -5 and about -1151. In certain
embodiments, for
stands that have three tubing engaging member, the angle between successive
stands 200 is
between about 100 and about 1100 or about 130 and about 180 . In other
embodiments, for
stands that have three tubing engaging member, the angle between successive
stands 200 is
between about 30 and about 90 or about 150 and about 180 . In other
embodiments, for
stands that have three tubing engaging member, the angle between successive
stands 200 is about
1800, a so-called staggered alignment. In other embodiments, for stands that
have three tubing
engaging member, the angle between successive stands 200 is about 90 . In
other embodiments,
for stands that have three tubing engaging member, the angle between
successive stands 200 is
about 60 . In other embodiments, for stands that have three tubing engaging
member, the angle
between successive stands 200 is about 30 . In other embodiments, for stands
that have three
CA 02731337 2011-02-07
-15-
tubing engaging member, the angle between successive stands 200 is about 15 .
The object of
the angle staggering of the stands 200 is to insure that the change or changes
to the tubing
passing through each successive stand 200 does not reinforce a particular
deformation causing
irregularities in the internal contour of the tubing. Thus, the stands of this
invention are
angularly staggered to reduce, minimize or even eliminate non-uniformity in
wall thickness of
the produced tubing. In this way, each successive stand 200 allows
deformations to the internal
contour of the tubing to be reduced, minimized or removed resulting in the
formation of a tubing
having a substantially circular internal contour and a substantially uniform
circumferential wall
thickness. Although each successive stand can be angularly staggered, in
certain embodiment,
a number of successive stand can be identically oriented followed by a number
of identically
oriented that are angularly staggered relative to the first number of
identically oriented stands.
Again, the goal of angular staggering is to produce a tubing the at any
location, the cross-
sectional contour of the tubing is substantially circular for both the outer
and inner diameter or
alternately, the wall thickness is substantially uniform at any cross-
sectional location of the
tubing, even though the wall thickness, inner diameter and/or outer diameter
of the tubing may
be the same or different at different locations along the length of the
tubing.
[0062] Referring now to Figures 16A B, a central cross-sectional view of a
stand 200 of this
invention is shown to include a housing 202 having a front and back panels 204
(only the back
panel is shown) and having mounted thereon a milling assembly 206. The milling
assembly 206
includes three rollers 208 designed to engage a tubing 100 as it passes
through the stand 200.
The milling assembly 206 has a closed state as shown in Figure 16A and an
opened state as
shown in Figure 16B. In the closed state, the roller 208 are designed to
engage substantially the
entire circumference of the tubing 100. Although the milling assemblies 206
can include from
two to five rollers, for the three roller configuration of Figures 16A-B, each
roller engages
substantially 1/3 of the circumference of the tubing 100. Of course, if the
number of rollers is
different, then the amount of the circumference engaged by each roller will be
360 divided by
the number of rollers.
[00631 Each roller 208 of the assembly 206 is mounted on a slidable mount 210
having front and
back guides 212 (only the back guides are shown) that travel in a groove 214
formed on the back
pane1204. The mount 210 includes a drive motor 216. The mount 210 is attached
to a shaft 218
of a solenoid or adjustment motor 220. The solenoid or motor 220 is designed
to transition the
mount 210 between its closed state and its opened state. The motor 220 is also
designed to
change the compression force acting on the tubing 100 by the three rollers
208. The slidable
mounts 210 are mounted on between a front and back circular plate 222 (only
the back plate is
CA 02731337 2011-02-07
-16-
shown) having an aperture 224 therethrough. The housing 202 also includes an
aperture an
aperture 226 therethrough. The motors 216 and 220 can be hydraulic or electric
and include
connectors 228 and 230, respectively, for connecting the motor to an electric
power source or
a hydraulic fluid source. Each roller 208 is mounted on a roller shaft 232
attached to a first
bearing 234 and a second bearing 236 that are driven by the motor 216. The
hydraulic or
electrical version of the stands 200 of these two figures can be constructed
so that the rotational
orientation of each stand relative to its immediate successor and predecessor
can be rotated by
any desired angle or they can be in either a Y-up or Y-down fixed
configuration. In either case,
the stands have either an alternating Y-up/Y-down configuration or successive
engaging
assemblies are rotated by an amount sufficient to produce a tubing with a
substantially circular
internal contour. The term Y-up means that one of the roller mounts is
oriented vertically down
so that the mounts for a Y. Y-down means that the roller mounts are rotated
180 to form an
upside down Y.
[0064] Looking now at Figure 17, another embodiment of a stand 250 of this
invention is shown
to include a mechanical drive system 252 (two are shown) and a three roller
mill assembly 254
mounted on a stand housing 253. The drive system 252 includes a motor 256 and
a main drive
shaft 258. The mill assembly 254 includes three rollers 260, each roller 260
is mounted in a
roller housing 262. The roller housings 262 includes guides 264 that allow the
roller housings
262 to be moved in and out via shafts 266 actuated by solenoids 268 or other
device that can
move the roller housings 262 in and out so that the assembly 254 can
transition between a close
configuration and an opened configuration. As in the embodiments of Figures
16A&B, the
closed configuration is characterized by the rollers 260 fully engaging the
tubing 100, while the
opened configuration is characterized by the rollers 260 fully disengaging the
tubing 100 so the
tubing 100 passes through the stand 200 without modification or passes through
the stand 200
during tubing 100 loading. The solenoids 268 in addition to move the roller
housing 262 in and
out and two also control the compression tension the rollers 260 exert on the
tubing 100. The
assembly 254 also includes gear system 270 designed to engage the drive shaft
258 so that the
three rollers 260 can be turned at the same rate to advance the tubing 100
though the stand 200.
The mechanical stand 250 is constrained due to design generally to a Y-up or Y-
down
configuration. Again, the stand 250 are generally staggered Y-up/Y-down to
ensure that a
substantially circular internal tubing contour is achieved. ' -
[0065] Referring now to Figures 18A-H, a variety of tubing types that can be
made using the
stands of this invention are shown. Looking at Figure 18A, the milling station
of this invention
can make tubing 300 having a uniform inner diameter ID, outer diameter OD and
wall thickness
CA 02731337 2011-02-07
-17-
WT as shown. As stated previously herein, the ability to make tubing having a
uniform or
constant wall thickness is difficult with traditional mills because the
compression stands tend to
cause the interior contour to assume a hexagonal configuration. Rotating the
stands relative
orientation tends to minimize or eliminate the hexagonal contouring leaving a
substantially
circular contour or a tubing have a substantially uniform wall thickness.
[0066] Looking at Figure 18B, the milling station of this invention can make
tubing 300 having
a uniform or constant outer diameter OD and a varying ID and a varying wall
thickness WT as
shown. The method for making a tapered wall tubing of Figure 18B is to having
successive
stands pulling the tubing with a greater force so that the tubing enters with
a given OD, ID and
WT and after passing through each stand the ID is increased while the WT is
decreased and the
OD stays the same. The amount of taper will depend on the speed that the
rollers are driven in
each stand at constant roller opening. Moreover, the stands do not all have to
operate under
different conditions, i.e., each successive stand further drawing the tubing,
but one stand can
draw while a number of following stands can simply remain at the constant ID,
OD and WT
produced by the drawing stand. This process can be continued so that drawing
occurs at only
a set number of stands with relaxation stands interposed therebetween. Again,
each stand can
give rise to a change generally between about 1% and about 10% of the ID, OD
and/or WT of
the tubing passing through each stand.
[0067] Looking at Figure 18C, the milling station of this invention can make
tubing 300 having
a varying inner diameter ID, a varying outer diameter OD and a constant wall
thickness WT.
This type of tubing is made by changing not only the drawing speed of the
stands as set by the
roller speed, but also the diameter of the opening and the force exerted on
the tubing at each
stand. Thus, the drawing speed and compressing force at each stand is set so
that the ID and OD
change, while maintaining a constant WT.
[0068] Looking at Figure 18D, the milling station of this invention can make
tubing 300
including a first non-tapered segment 302 having a constant first inner
diameter ID1, a constant
first outer diameter OD1 and a constant wall thickness WT. The tubing 300 also
includes a
second segment 304 having varying inner diameter IDv and a varying outer
diameter ODv and
the same WT. The tubing 300 also includes a third segment 306 having a
constant second inner
diameter ID2, a constant second outer diameter OD2 and a constant wall
thickness WT. This
type of tubing is made by controlling the stands settings to make tubing
having the
characteristics of the third segment, then changing the stand settings to
produce tubing having
the characteristics of the second segment that tapers at a controlled rate,
and finally, changing
the stand settings to produce tubing having the characteristics of the third
tubing segment.
CA 02731337 2011-02-07
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[0069] Looking at Figure 18E, the milling station of this invention can make
tubing 300 having
a varying inner diameter ID, a varying outer diameter OD and a varying wall
thickness WT.
This type of tubing is made by controlling the stand settings so that all
three variable ID, OD and
WT change at a controlled rate, by changing the drawing speed (the turning
rate of the rollers
in the stands), the compressive force acting on the tubing as it passes
through each stand and the
opening size as the tubing passes through each stand.
[0070] Looking at Figure 18F, the milling station of this invention can make
tubing 300
including a first non-tapered segment 302 having a constant inner diameter ID,
a constant first
outer diameter OD1 and a constant first wall thickness WT1. The tubing 300
also includes a
second segment 304 having the inner diameter ID and a varying outer diameter
ODv and a
varying wall thickness WTv. The tubing 300 also includes a third segment 306
having a
constant inner diameter ID, a constant second outer diameter OD2 and a
constant second wall
thickness WT2. This type of tubing is made by setting the stands to make a
tubing having the
tubing of the third segment, then changing the stand settings to produce the
second segment that
tapers the tubing, and finally, changing the stand settings to produce the
third segment.
[0071] Looking at Figure 18G, the milling station of this invention can make
tubing 300
including a fast non-tapered segment 302 having a constant inner diameter ID,
a constant first
outer diameter OD1 and a constant first wall thickness WT1. The tubing 300
also includes a
first tapered segment 304 having the inner diameter ID and a first varying
outer diameter ODvl
and a first varying wall thickness WTv1. The tubing 300 also includes a second
non-tapered
segment 306 having the constant inner diameter ]OD, a constant second outer
diameter OD2 and
a constant second wall thickness WT2. The tubing 300 also includes a second
tapered segment
308 having the inner diameter ID and a second varying outer diameter ODv2 and
a second
varying wall thickness WTv2. The tubing 300 also includes a third non-tapered
segment 310
having the constant inner diameter ID, a constant third outer diameter OD3 and
a constant third
wall thickness WT3. The first and third outer diameters OD1 and OD3 and the
first and third
wall thicknesses WT1 and WT3 can be the same or different, while the first and
the second
varying outer diameters ODvl and ODv2 and the first and second varying wall
thicknesses
WTvl and WTv2 can be the same or different. This type of tubing is made by
setting the stands
to make a tubing having the characteristics of the third non tapered segment.
The stand settings
are then. changed to produce tubing having the characteristics of the second
varying segment.
The stand settings are changed to produce tubing having the characteristics of
the second non-
tapered segment. The stand settings are changed to produce tubing having the
characteristics of
the first varying segment. Finally, the stand setting are changed to produce
tubing having
CA 02731337 2011-02-07
-19-
characteristics of the first non-tapered segment. Of course, the segments can
have variable inner
diameters as well.
[00721 Looking at Figure 18H, the milling station of this invention can make
tubing 300
including a first non-tapered segment 302 having a constant first inner
diameter ID1, a constant
first outer diameter OD1 and a constant wall thickness WT. The tubing 300 also
includes a first
tapered segment 304 having a first varying inner diameter IDvl and a first
varying outer
diameter ODvl and the wall thickness WT. The tubing 300 also includes a second
non-tapered
segment 306 having a second constant inner diameter ID2, a constant second
outer diameter
OD2 and the wall thickness WT. The tubing 300 also includes a second tapered
segment 308
having a second varying inner diameter IDv2 and a second varying outer
diameter ODv2 and
the wall thickness WT. The tubing 300 also includes a third non-tapered
segment 310 having
a third constant inner diameter ID3, a constant third outer diameter OD3 and
the wall thickness
WT. The first and third outer diameters OD1 and OD3 and the first and third
inner diameters
IDl and ID3 can be the same or different, while the first and the second
varying outer diameters
ODv1 and ODv2 and the first and second varying inner diameters IDvl and IDv2
can be the
same or different. This type of tubing is made by setting the stands to make a
tubing having the
characteristics of the third non-tapered segment. The stand settings are then
changed to produce
tubing having the characteristics of the second varying segment. The stand
settings are changed
to produce tubing having the characteristics of the second non-tapered
segment. The stand
settings are changed to produce tubing having the characteristics of the first
varying segment.
Finally, the stand setting are changed to produce tubing having
characteristics of the first non-
tapered segment. Of course, the segments can have variable wall thicknesses as
well.
[00731 Even though three characteristics are discussed with relationship to
the produced tubing,
only two need be controlled as the third is a fixed once the other two
characteristics are set, i.e.,
once OD and ID are set, WT is completely defined. It should also be recognized
that the tapered
segments can be produced with any rate of taper. Thus, the taper can be a
percentage per a given
length of produced tubing. The percentage per length is set by the maximum
change that can
be imparted to the tubing when all stands are operating at their maximum speed
and
compression. By changing the stand settings, any degree of tapering can be
achieve between no
tapering and a maximum amount of tapering corresponding to the maximum change
that each
of the stands can produce. Of course, the maximum change that can be produced
will be
controlled by the total number of stands in the mill reduction station and on
the maximum
change the each stand can impart to the tubing as it passes through each
stand. Of course, each
stand is designed to be held at a temperature so that the metal properties are
optimum for forging
CA 02731337 2011-10-12
-20-
without imparting to much stress and/or strain into the metal or causing
morphological
changes in the metallurgical properties of the metal out of which the tubing
is made.
[00741 The tubing configuration described above can be made from a single roll
of flat stock
or from one or more rolls of flat stock butt welding according to any of the
butt welding
formate described above including the bias butt welds as U.S. Patent Nos.
4,863,091 and
5,191,911.
100751 Therefore, it maybe observed to a person of skill in the art that the
present invention
and the embodiments disclosed herein are appropriate to carry out the
objectives and to
demonstrate the features set forth above. Certain alterations may be made in
the subject matter
without departing from the spirit and the scope of this invention. It is
realized that changes are
possible within the scope of this invention.
[00761 While this invention has been described fully and completely, it should
be understood
that the invention may be practiced otherwise than as specifically described.
Although the
invention has been disclosed with reference to its preferred embodiments, from
reading this
description those of skill in the art may appreciate changes and modification
that may be
made which do not depart from the scope and spirit of the invention.
